Optical semiconductor elements, such as light emitting diodes (LED), are used as indicators or light sources. Recently, their output is higher and their wavelength is shorter, so that there is a problem that resin materials present near the optical semiconductor elements degrade due to light to turn yellow and, therefore, light output lowers.
The following Patent Literature 1 discloses, as a resin composition for encapsulating optical semiconductors, an epoxy resin composition in a B stage which comprises an epoxy resin, a curing agent, and a curing promoter. It describes that bisphenol A epoxy resin or bisphenol F epoxy resin is mainly used as the epoxy resin and triglycidyl isocyanate may be used. However, the afore-mentioned composition has the aforesaid yellowing problem, particularly when a semiconductor element is lightened at a high temperature or for a long time.
Patent Literature 2 discloses a composition which comprises an epoxy resin derived from isocyanuric acid, as a heat-resistant and light-resistant epoxy resin composition for encapsulating light emitting elements. However, light resistance of the composition is insufficient, again.
Patent Literature 3 discloses a resin composition for encapsulating LED devices, which composition comprises an organopolysiloxane having a weight average molecular weight of 5×102 or higher and a condensation catalyst. However, the composition is directed to applications where high transparence is required, rather than to applications where white pigments are used, such as reflectors.
Meanwhile, recently, sizes of molded package become bigger, for instance, in Matrix Array Package (MAP) method and, therefore, warpage in curing of an encapsulating resin becomes a serious problem. Large warpage causes various malfunctions in a package carrying step or a package cutting step. The afore-mentioned compositions are unsatisfactory in this respect, either.
Patent Literature 1: Japanese Patent Application Laid-Open Hei-02-189958
Patent Literature 2: Japanese Patent Application Laid-Open 2005-306952
Patent Literature 3: Japanese Patent Application Laid-Open 2006-77234